1. Field of the Invention
This invention relates to asphalt and heavy fuel oil production techniques. This invention particularly relates to asphalt and heavy fuel oil production employing chemical additives.
2. Background of the Art
“Kerogen” is generally defined in the art of hydrocarbon production as a solid, insoluble hydrocarbon that has been converted by natural degradation (e.g., by diagenesis) and that principally contains carbon, hydrogen, nitrogen, oxygen, and sulfur. Coal and oil shale are typical examples of materials that contain kerogens. “Bitumen” is generally defined in the art as a non-crystalline solid or viscous hydrocarbon material that is substantially soluble in carbon disulphide.
“Oil” is generally defined as a fluid containing a complex mixture of hydrocarbons. During a refining process, oil is converted into a number of products. For example, gasoline is one such product and is a mixture of low viscosity and volatile hydrocarbons. Lubricating oil is another hydrocarbon product and has higher viscosity and lower volatility. It is usually very pure and has a very low amount of corrosive materials.
Fuel oils, on the other hand, tend to be products produced by first removing the premium components such as those just listed from crude oil. The residual products are then subjected to processes such as cracking to produce more of the premium products. Finally, when it becomes uneconomical to further treat the residue, they are then sold according to their viscosity and other physical properties.
The ASTM (American Society for Testing and Materials) employs six grades for characterizing fuel oils. Heavy fuel oils are those in grades 4, 5 and 6. Grade 4 is typical commercial fuel oil and can often be used in burners without the need for preheating. Grade 5 fuel oils are typically higher in viscosity and lower in volatility and are sometimes referred to as “Bunker B” while the very heavy fuel oils in Grade 6, such as “Bunker C,” have even greater viscosity and lower volatility.
The heavy and especially the very heavy fuel oils are often employed in applications where high viscosity can be tolerated and the use of preheating can be employed. For examples. Bunker C is often used in large ships. Bunker B is sometimes employed in applications that would otherwise burn coal. Any of these grades, but especially the Bunker B and C oils, is likely to contain a substantial amount of sulfur and sulfur compounds.
Materials which are even higher in viscosity and lower in volatility than fuel oils, but are not a solid such as coke, are often also referred to in the art as bitumen or asphalt and further include many of the non-hydrocarbon components of oil, including elemental sulfur and sulfur containing compounds. These bitumen and bitumen like products have a surprising number of uses including but not limited to membranes useful for waterproofing roofs, shingle construction, and road construction. Heavy fuel oils, on the other hand, are often employed in applications where high viscosity can be tolerated and the use of preheating can be employed.
Hydrogen sulfide, a sulfur bearing compound, may be a safety and environmental concern to the petroleum industry. Vacuum tower bottoms (VTB) used in the production of bitumen and heavy fuel oil often contain high levels of hydrogen sulfide that pose significant danger to individuals involved in its production and handling. While hydrogen sulfide is often removed from refined fuels by refinery processes, less valuable products used for fuel oil and asphalt production sometimes do not receive additional processing to remove hydrogen sulfide. Hydrogen sulfide levels in such products can be aggravated by the high temperatures (sometimes above 300° F.) as these temperatures may generate additional hydrogen sulfide from the cracking of sulfur compounds inherent in the heavy oil.
The reduction of hydrogen sulfide in asphalt and heavy fuel oil is therefore an important consideration that presents unique challenges to the petroleum refining industry.